Wellllllllll, Let me see. The two jobs are COMPLETELY different so take a long look before you make any changes.
Do you like being an airline pilot? Is that what you've been striving for? If so, DO NOT go to a fractional.
As an FO at a fractional, you will be doing a lot of things you will never do at an airline, ie,
Load Bags, load/arraigned catering, wipe the lav seat, clean tray tables and vacuum the floor, just to name a few.
You know how you swap legs at the airline? Well, forget that at some fractional's. You will fly the empty legs.
Now, some upsides of fractionals...
Different places most every day, nicer hotels(but you won't know how long you'll be there), Good crew food, better schedules and, most likely, no commuting on your own time.
Big decision man...I went to a fractional from a regional and wish I hadn't. Oh well, Waaaa for me. Just do what your doing now, ask alot of questions and think hard. Once you lose that seniority number, its tough to go back.
Hope that helped.